The present invention relates essentially to a seal for a brake master cylinder, particularly for a motor vehicle.
Motor vehicle brake controls generally comprise a brake pedal acting on a master cylinder to transmit, via a hydraulic circuit, a liquid pressure to receivers that brake the various wheels.
The brake pedal acts on a piston sliding axially in a body comprising a seal comprising a lip which presses against the piston, in order to separate a rear volume containing a reserve of liquid at atmospheric pressure from a front volume comprising a chamber pressurized by the displacement of this piston.
A brake master cylinder of this type is described in U.S. Pat. No. 6,272,858 B1, which has a circular seal with two lips. An inner lip surrounds the piston providing dynamic sealing. When the piston is at rest in the rear position, the inner lip enters a piston groove which has a shallow depth and gently inclined side walls.
In this rest position of the piston, a radial drilling formed in the piston and opening into the groove becomes positioned behind the inner lip of the lip seal to place the pressure chamber in communication with the reserve of liquid, and if necessary readjust the volume of the hydraulic circuit.
The lip seal is wedged axially in an annular housing of the body surrounding the piston, and comprises an outer lip which presses against a cylindrical bottom of this annular housing, to provide static sealing between the pressure chamber and the rear volume.
One main disadvantage with this master cylinder is that at the static sealing lip, small solid particles may, as a result of movements of the fluid when the pressure circuit is being topped up, for example, become lodged under this lip and remain trapped by the lip which is constantly pressed against the outside diameter in a static manner. The particles thus lodged under the lip may ultimately cause leaks as the lip is no longer evenly applied to the surface opposite.